The invention relates to a cutting tool or cutting insert and to a method for producing a cutting insert or a cutting tool which has a wear-resistant coating built up in multiple layer.
Cutting tools are subject to various stresses in operation that over time lead to wear. Wear means both the wearing down of chip faces and flanks and breakage of cutting edges. Furthermore, under conditions of heavy stress high temperatures also occur, which can cause diffusion wear and oxidation wear of edges and faces of the cutting tool. To reduce wear especially at high machining capacities, various coatings of cutting tools or cutting inserts have been developed.
For example, from European Patent Disclosure EP 0 786 536 A1, a hard metal cutting insert is known that is provided with a multilayer coating. The coating has a thickness of 3 to 20 xcexcm and is formed on a hard metal body by chemical or physical vapor deposition processes (CVD or PVD). The coating contains an aluminum oxide layer with a very low proportion of chlorine.
The aluminum oxide layer has a relatively great hardness. It also acts as an oxidized surface layer and at the same time as an oxidation protectant for underlying layers and is thus especially well suited to tools that are subject to tribochemical attack. It acts as a protectant against tribochemical wear processes such as diffusion and oxidation and also acts as thermal insulation and thus protects against plastic deformation.
European Patent Disclosure EP 0 736 615 A2 also proposes an aluminum oxide layer as an outermost layer of a multilayer coating of a cutting tool. Between the aluminum oxide layer and the actual hard metal body, a plurality of layers acting as intermediate coatings or underlying layers are formed. The substrate layer that is in immediate contact with the aluminum oxide layer is a titanium carbonitride oxide layer with a thickness of between 0.1 and 2 xcexcm and a needle-like crystal structure. Under this layer, one or more layers with a columnar crystal structure, composed of the same chemical elements, are formed.
The adherence of the aluminum oxide layer to the substrate is one essential factor. It is especially stressed upon plastic deformation and in interrupted cutting (milling, turning on a lathe, drilling) of steel and casting materials, especially such high-strength materials as 42CrMo4V and 56NiCrMoV7.
To improve the adherence of an aluminum oxide layer to the applicable underlying layers, U.S. Pat. No. 5,958,569 proposes a titanium carbonitride bonding layer between an outer aluminum oxide layer and a titanium nitride layer located beneath it. The bonding layer is meant to form interlocking microscopic fingers between the oxide coating and the metal carbonitride coating.
With this as the point of departure, it is the object of the invention to improve the adherence of an oxide layer (preferably an aluminum oxide layer) to underlying layers in cutting tools, cutting inserts, or the like.
This object is attained by the present invention.
The Periodic Table groups refer especially to the following elements: (the heavier elements of these groups not listed here would normally not be used):
Group III: B, Al, Sc, Y, In, La and Tl;
Group IV : C, Si, Ti, Ge, Zr, Sn, Hf and Pb;
Group V : N, P, V, As, Nb, Sb, Ta and Bi; and
Group VI: O, S, Cr, Se, Mo, The, W and Po.
The machining tool and cutting insert according to the invention have an aluminum oxide layer, which is retained on the underlying coatings by means of a bonding layer. The underlying coating is for example a titanium nitride, titanium carbide, or titanium carbonitride layer, and in addition to or in place of the titanium, the layer can also contain still other metals of Group IV, V or VI of the periodic system of Chemical Elements. The bonding layer firmly holds the aluminum oxide layer on the substrate and thus prevents or inhibits abrasion or breakage, flaking off or peeling off of the aluminum oxide layer. The improved adherence of the aluminum oxide layer to the substrate allows a heavier load on the machining tool or cutting insert and a longer service life thereof possible.